[Cocci] Coccinelle can't tell that "current" has type "struct task_struct *"

[Josh Triplett]

In the Linux kernel, "current" refers to the current task, of type
"struct task_struct *", by way of a stack of (sometimes arch-specific)
macros.  For instance, arch/x86/include/asm/current.h defines current as
get_current(), an inline function returning "struct task_struct *".
Other architectures, as well as asm-generic, use variations on the same
theme with varying depths of macros.

However, coccinelle doesn't seem to manage to figure out the type of
current, because rules defined with @@struct task_struct *task;@@ don't
match current.

I can work around this by writing a duplicate set of rules with
@@identifier current;@@, but I'd rather not have to introduce that
duplication.

For a test case, try the following semantic patch:

@@ struct task_struct *task; @@
- (task)->pid == 0
+ is_idle_task(task)

@@ struct task_struct *task; @@
- (task)->pid != 0
+ !is_idle_task(task)


And the following test file:

#include <linux/sched.h>
extern struct task_struct *t;
void context(void)
{
        if (t->pid)
                do_something();
        if (current->pid)
                do_something();
}


Coccinelle successfully patches the first condition, but not the second.

- Josh Triplett
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